The present invention relates to an optical encoder to be attached to a rotating axis of a servo motor, etc., in particular, a shape of a light receiving window which is disposed above a slit into which light comes.
An optical rotary encoder is such that a code pattern is provided on a rotary disk constructed of glass, etc., light from a light emitting element such as an LED, etc., is made incident into the code pattern, light transmitted through or reflected from the code pattern is received directly by a light receiving element such as a photo diode, etc., or via a light receiving window. And a minute current of the light receiving element is amplified by a circuit substrate and is converted to adjusted electric signals, wherein the electric signals are multiplied, interpolated or pulsated to detect the rotating speed or rotating position of the abovementioned disk.
In the above rotary encoder, the quantity of light received by respective light receiving elements is not the same, and differences may arise in the minute current in the light receiving elements. Therefore, in the case where the minute current is amplified by the circuit substrate and converted to electric signals, a difference occurs in the degree of amplification in the respective light receiving elements.
Where electric signals are multiplied, interpolated or pulsated with respect to progress of high accuracy, if there is a difference in the respective basic signals, a problem in the frequency characteristics arises, which causes a lowering of the position precision at a high speed operation.
Therefore, the present invention was developed to solve the above problem, and it is therefore an object of the invention to provide an encoder that can prevent the position precision at a high speed operation from deteriorating.
An encoder according to the invention is an encoder having a code pattern provided on a rotary disk, which detects the rotation speed and rotational position of the rotary disk by receiving light coming from a light emitting element and transmitted through or reflected from the code pattern by the light receiving element; wherein a fixed slit which is disposed between the rotary disk and the light receiving element so that a plurality of light receiving windows through which light reflected from or transmitted through the code pattern passes is disposed so as to have a difference in phase at different positions in the radial direction of the rotary disk; the length of the light receiving windows in the radial direction is set so as to gradually become shorter from the inner peripheral side toward the outer peripheral side; and the opening area of the light receiving windows at the inner peripheral side of the fixed slit is set to be equal to that at the outer peripheral side.
An encoder having a code pattern provided on a rotary disk, which detects the rotation speed and rotation position of the rotary disk by receiving light transmitted through or reflected from the code pattern by light receiving elements; wherein the light receiving elements have a plurality of light receiving portions to receive light, coming from a light emitting element, transmitted from or reflected from the code pattern, which are disposed so that it has a difference in phase in different positions in the radial direction of the rotary disk; the length of the rotary disk of the light receiving portions in the radial direction is set so as to gradually become shorter from the inner peripheral side toward the outer peripheral side; the area of the light receiving portion at the inner peripheral side of the light receiving element is set to be equal to that at the outer peripheral side.
According to the encoder of the invention, since the length, of the light receiving window or rotary disk having the shape of the light receiving portions, in the radial direction is set so as to gradually become shorter from the inner peripheral side to the outer peripheral side, the area of the light receiving windows or the light receiving portion can be set to be the same regardless of the position of the rotary disk in the radial direction.